Method for in situ tailoring the metallic component of ceramic articles

ABSTRACT

There is disclosed a method for producing a self-supporting ceramic body by oxidation of a molten precursor metal with a vapor-phase oxidant to form an oxidation reaction product and inducing a molten flux comprising said molten precursor metal through said oxidation reaction product. A second metal is incorporated into said molten flux during the oxidation reaction. The resulting ceramic body includes sufficient second metal such that one or more properties of said ceramic body are at least partially affected by the presence and properties of said second metal.

This is a continuation of copending application Ser. No. 06/908,454filed on Sept. 17, 1986 now abandoned.

FIELD OF THE INVENTION

This invention relates to a method for producing self-supporting ceramicbodies, formed as the oxidation reaction product of a precursor metaland a vapor-phase oxidant, and having a metallic component including asecond metal introduced during formation of the ceramic body to impartcertain properties to the ceramic body. The invention also relates tosuch ceramic bodies produced thereby.

BACKGROUND OF THE INVENTION AND COMMONLY OWNED PATENT APPLICATIONS

In recent years, there has been an increasing interest in the use ofceramics for structural applications historically served by metals. Theimpetus for this interest has been the superiority of ceramics withrespect to certain properties, such as corrosion resistance, hardness,modulus of elasticity, and refractory capabilities, when compared withmetals.

Current efforts at producing higher strength, more reliable, and tougherceramic articles are largely focused upon (1) the development ofimproved processing methods for monolithic ceramics and (2) thedevelopment of new material compositions, notably ceramic matrixcomposites. A composite structure is one which comprises a heterogeneousmaterial, body or article made of two or more different materials whichare intimately combined in order to attain desired properties of thecomposite. For example, two different materials may be intimatelycombined by embedding one in a matrix of the other. A ceramic matrixcomposite structure typically comprises a ceramic matrix whichincorporates one or more diverse kinds of filler materials such asparticulates, fibers, rods, and the like.

There are several known limitations or difficulties in substitutingceramics for metals, such as scaling versatility, capability to producecomplex shapes, satisfying the properties required for the end useapplication and costs. Several copending patent applications and patentsassigned to the same owner as this application (hereinafter referred toas Commonly Owned Patents and Patent Applications), overcome theselimitations or difficulties and provide novel methods for reliablyproducing ceramic materials, including composites. The method isdisclosed generically in commonly owned U.S. Pat. No. 4,713,360, whichissued on Dec. 15, 1987 from copending U.S. application Ser. No.818,943, filed Jan. 15, 1986, which was a continuation-in-part of Ser.No. 776,964, filed Sept. 17, 1985, and now abandoned which was acontinuation-in-part of Ser. No. 705,787, filed Feb. 26, 1985and nowabandoned which was a continuation-in-part of U.S. application Ser. No.591,392, filed Mar. 16, 1984, and now abandoned all in the names of MarcS. Newkirk et al and entitled "Novel Ceramic Materials and Methods forMaking the Same". This Patent discloses the method of producingself-supporting ceramic bodies grown as the oxidation reaction productfrom a parent precursor metal Molten metal is reacted with a vapor-phaseoxidant to form an oxidation reaction product, and the metal migratesthrough the oxidation product toward the oxidant thereby continuouslydeveloping a ceramic polycrystalline body which can be produced havingan interconnected metallic component. The process may be enhanced by theuse of an alloyed dopant, such as is used in the case of oxidizingaluminum doped with magnesium and silicon for oxidation reaction in airto form alpha-alumina ceramic structures. This method was improved uponby the application of dopant materials to the surface of the precursormetal, as described in commonly owned U.S. patent application Ser. No.220,935, filed June 23, 1988, which issued on Aug. 1, 1989, as U.S. Pat.No. 4,853,352, that was a continuation of Ser. No. 822,999, filed Jan.27, 1986, and now abandoned which was a continuation-in-part of Ser. No.776,965, filed Sept. 17, 1985, and now abandoned which was acontinuation-in-part of Ser. No. 747,788, filed June 25, 1985, and nowabandoned which was a continuation-in-part of Ser. No. 632,636, filedJuly 20, 1984, and now abandoned all in the names of Marc S. Newkirk etal and entitled "Methods of Making Self-Supporting Ceramic Materials".

This oxidation phenomenon was utilized in producing ceramic compositebodies as described in commonly owned U.S Pat. No. 4,851,375, whichissued on July 25, 1989, from U.S. patent application Ser. No. 819,397,filed Jan. 17, 1986, which was a continuation-in-part of Ser. No.697,876, filed Feb. 4, 1985, and now abandoned both in the names of MarcS. Newkirk et al and entitled "Composite Ceramic Articles and Methods ofMaking Same". These applications and Patent disclose novel methods forproducing a self-supporting ceramic composite by growing an oxidationreaction product from a precursor metal into a permeable mass of filler,thereby infiltrating the filler with a ceramic matrix. The resultingcomposite, however, has no defined or predetermined geometry, shape, orconfiguration.

A method for producing ceramic composite bodies having a predeterminedgeometry or shape is disclosed in the commonly owned and copending U.S.patent application Ser. No. 338,471, filed on Apr. 14, 1989, which is acontinuation of U.S. patent application Ser. No. 861,025, filed on May8, 1986 and now abandoned in the names of Marc S. Newkirk, et al andentitled, "Shaped Ceramic Composites and Methods of Making the Same". Inaccordance with the method in these U.S. patent applications, thedeveloping oxidation reaction product infiltrates a permeable preform inthe direction towards a defined surface boundary. It was discovered thathigh fidelity is more readily achieved by providing the preform with abarrier means, as disclosed in commonly owned U.S. Pat. No. 4,923,832,which issued on May 8, 1990, from U.S. patent application Ser. No.861,024, filed on May 8, 1986 in the names of Marc S. Newkirk, et al andentitled, "Method of Making Shaped Ceramic Composites with the Use of aBarrier". This method produces shaped self-supporting ceramic bodies,including shaped ceramic composites, by growing the oxidation reactionproduct of a precursor metal to a barrier means spaced from the metalfor establishing a boundary or surface. Ceramic composites having acavity with an interior geometry inversely replicating the shape of apositive mold or pattern is disclosed in commonly owned U.S. Pat. No.4,828,785, which issued on May 9, 1989, from U.S. patent applicationSerial No. 823,542, filed on Jan. 27, 1986, and in U.S. Pat. No.4,859,640, which issued on Aug. 22, 1989, from U.S. patent applicationSer. No. 896,157, filed on Aug. 13, 1986.

The aforementioned Commonly Owned Patent Applications and Patentsdisclose methods for producing ceramic articles which overcome some ofthe traditional limitations or difficulties in producing ceramicarticles as substitutes for metals in end-use applications.

Common to each of these Commonly Owned Patent Applications and Patentsis the disclosure of embodiments of a ceramic body comprising anoxidation reaction product interconnected in one or more dimensions(usually in three dimensions) and one or more metallic constituents orcomponents. The volume of metal, which typically includes non-oxidizedconstituents of the parent metal and/or metal reduced from an oxidant orfiller, depends on such factors as the temperature at which theoxidation reaction product is formed, the length of time at which theoxidation reaction is allowed to proceed, the composition of the parentmetal, the presence of dopant materials, the presence of reducedconstituents of any oxidant or filler materials, etc. Some of themetallic components are isolated or enclosed, but also a substantialvolume percent of metal will be interconnected and accessible, orrendered accessible, from an external surface of the ceramic body. Ithas been observed for these ceramic bodies that this metal-containingcomponent or constituent (both isolated and interconnected) can rangefrom about 1 to about 40 percent by volume, and sometimes higher. Themetallic component can impart certain favorable properties to, orimprove the performance of, the ceramic articles in many productapplications. For example, the presence of metal in the ceramicstructure may have a substantial benefit with respect to impartingfracture toughness, thermal conductivity, resilience or electricalconductivity to the ceramic body.

The present invention discloses a method for tailoring the constituencyof the metallic component (both isolated and interconnected) of suchceramics during formation of the ceramic body to impart one or moredesirable characteristics to the resulting ceramic product. Thus,product design for the ceramic body is advantageously achieved byincorporating the desired metallic component in situ, rather than froman extrinsic source or by post-forming.

The entire disclosures of all of the foregoing Commonly Owned PatentApplications and Patents are expressly incorporated herein by reference.

DEFINITIONS

As used herein in the specification and the appended claims, the termsbelow are defined as follows:

"Ceramic" is not to be unduly construed as being limited to a ceramicbody in the classical sense, that is, in the sense that it consistsentirely of non-metallic and inorganic materials, but rather refers to abody which is predominantly ceramic with respect to either compositionor dominant properties, although the body contains minor or substantialamounts of one or more metallic constituents (isolated and/orinterconnected), most typically within a range of from about 1-40% byvolume, but may include still more metal.

"Oxidation reaction product" means one or more metals in any oxidizedstate wherein the metal(s) has given up electrons to or shared electronswith another element, compound, or combination thereof. Accordingly, an"oxidation reaction product" under this definition includes the productof reaction of one or more metals with an oxidant such as oxygen,nitrogen, a halogen, sulphur, phosphorus, arsenic, carbon, boron,selenium, tellurium, and compounds and combinations thereof, forexample, methane, oxygen, ethane, propane, acetylene, ethylene,propylene (the hydrocarbon as a source of carbon), and mixtures such asair, H₂ /H₂ O and CO/CO₂, the latter two (i.e., H₂ /H₂ O and CO/CO₂)being useful in reducing the oxygen activity of the environment.

"Vapor-phase oxidant", which identifies the oxidant as containing orcomprising a particular gas or vapor, means an oxidant in which theidentified gas or vapor is the sole, predominant or at least asignificant oxidizer of the precursor metal under the conditionsobtained in the oxidizing environment utilized. For example, althoughthe major constituent of air is nitrogen, the oxygen content of air isthe sole oxidizer for the precursor metal because oxygen is asignificantly stronger oxidant than nitrogen. Air therefore falls withinthe definition of an "oxygen-containing gas" oxidant but not within thedefinition of a "nitrogen-containing gas" oxidant as those terms areused herein and in the claims. An example of a "nitrogen-containing gas"oxidant is "forming gas", which typically contains about 96 volumepercent nitrogen and about 4 volume percent hydrogen.

"Precursor metal or Parent metal" refers to the metal which reacts withthe vapor-phase oxidant to form the polycrystalline oxidation reactionproduct, and includes that metal as a relatively pure metal or acommercially available metal with impurities; and when a specified metalis mentioned as the precursor metal, e.g. aluminum, the metal identifiedshould be read with this definition in mind unless indicated otherwiseby the context.

"Second or foreign metal" means any suitable metal, combination ofmetals, alloys, intermetallic compounds, or source of either, which is,or is desired to be, incorporated into the metallic component of aformed ceramic body in lieu of, in addition to, or in combination withunoxidized constituents of the precursor metal This definition includesintermetallic compounds, alloys, solid solutions or the like formedbetween the precursor metal and a second metal.

"Flux" of molten metal means the flow or transport of molten metalwithin the oxidation reaction product, induced by the processconditions. "Flux" as used herein is not meant to define a substance asused in reference to classical metallurgy.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method forproducing a self-supporting ceramic body by the oxidation of a precursormetal wherein said body comprises the oxidation reaction product of amolten precursor metal and vapor-phase oxidant, and a metalliccomponent. A second or foreign metal is introduced or incorporated intothe metallic component of the ceramic body during the formation of theceramic body in a quantity sufficient to at least partially affect oneor more properties of the ceramic body.

Generally, in the method for producing a self-supporting ceramic body bythe oxidation of a precursor metal, the precursor metal is heated in thepresence of a vapor-phase oxidant to form a body of molten metal. Themolten precursor metal is reacted with the oxidant, at a suitabletemperature, to form an oxidation reaction product, which product ismaintained at least partially in contact with, and extends between, thebody of molten precursor metal and the vapor-phase oxidant. At thistemperature, molten precursor metal is transported through the oxidationreaction product towards the vapor-phase oxidant. During the process, asecond or foreign metal is incorporated into the flux of molten metal(described below in detail) and thence into the resulting metalcomponent of the ceramic product. The resulting metallic constituent,comprising molten precursor metal and foreign metal, is transportedthrough the oxidation reaction product, and the precursor metal oxidizesas it contacts the vapor-phase oxidant thereby continuously developing aceramic polycrystalline body. The oxidation reaction is continued for atime sufficient to form a self-supporting ceramic body comprising theoxidation reaction product and a metallic component. That metalliccomponent comprises nonoxidized constituents of the precursor metal andthe second or foreign metal which is present in a significant quantitysuch that one or more properties of the ceramic body are at leastpartially effected by the presence and/or properties of the second orforeign metal. By reason of the process of this invention, the ceramicproduct exhibits one or more predetermined or desired properties.

In accordance with the present invention, the second or foreign metal isintroduced into the flux of molten precursor metal during the formationof the ceramic body, and is transported with molten precursor metalthrough the oxidation reaction product. A portion of the precursor metalreacts with the vapor-phase oxidant to form the oxidation reactionproduct while the foreign metal remains substantially unoxidized by thevapor-phase oxidant, and typically is dispersed throughout the metalcomponent. Upon formation of the ceramic body, the second or foreignmetal, as a constituent of the metallic component, is an integral partof the ceramic product thereby altering or improving one or moreproperties of the product.

In another aspect of the present invention, a second metal isincorporated into the flux of molten precursor metal and thence into theceramic body. During the process, molten precursor metal is converted tooxidation reaction product, and the oxidation reaction is continued fora time sufficient to deplete the amount of precursor metal in the fluxof molten metal, relative to the amount of second metal present in theflux, thereby leading to the formation of one or more desired metallicphases comprising the second metal and precursor metal within themetallic component of the ceramic body. The desired phase formation canoccur at or within the range of the reaction temperature, onpost-process cooling or heat treatment of the ceramic body, or duringservice or application of the ceramic product fabricated in accordanceherewith. The resulting ceramic body has a metallic component havingtherein incorporated one or more metallic phases which impart one ormore predetermined desired properties to the ceramic product.

The second or foreign metal may be provided for incorporation into theflux of molten metal or ceramic body by any one of several means, or acombination of means. The second or foreign metal may be alloyed withthe precursor metal in a pre-process step, which is intended to includeemploying commercially available precursor metal alloys having a desiredcomposition, or may be applied onto one or more surfaces of theprecursor metal, preferably the growth surface of the precursor metal.During the oxidation reaction process, the second or foreign metal isincorporated into the flux of molten metal, transported into theoxidation reaction product, and becomes an integral part of theinterconnected metallic component and thus of the ceramic body.

In another embodiment, wherein a composite is formed, and the oxidationreaction product is grown into a mass of filler material or a shapedpreform, the second metal may be provided by admixing it with the filleror preform material, or may be applied to one or more of its surfaces.As the oxidation reaction product infiltrates the filler material, andthus the molten metal is transported through the developing oxidationreaction product, the molten precursor metal contacts the second metal(or its source). On contact, the second metal, or some portion thereof,is introduced or incorporated into the flux of molten precursor metaland transported along with it into the ceramic matrix. The precursormetal, or a portion thereof, continues to be oxidized by the vapor-phaseoxidant at the interface between the vapor-phase oxidant and previouslyformed oxidation reaction product, while the second metal is beingtransported in the flux within the formed composite. Hence, the secondor foreign metal is incorporated into the flux of molten metal.

In still another embodiment, the second or foreign metal is provided inthe form of a compound or mixture which reacts with the molten metal,and/or dissociates under the process conditions, to liberate the secondmetal which is then introduced or incorporated into the flux of moltenmetal. Such a compound, for example, may be a metal oxide which isreducible by the molten precursor metal. This compound may be applied ina layer on top of the precursor metal body, or admixed with or appliedto a filler or preform material.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In accordance with the present invention, the precursor metal, which maybe doped (as explained below in greater detail), and is the precursor tothe oxidation reaction product, is formed into an ingot, billet, rod,plate, or the like; and is placed into a setup of an inert bed, crucibleor other refractory container. It has been discovered that a second orforeign metal can be introduced into the flux of molten precursor metalduring formation of the ceramic body. The resulting constituencycomprising precursor metal and second metal is transported through theoxidation reaction product by the flux of molten metal which includescapillary transport of the molten metal, as described in the CommonlyOwned Patent the Patents Applications. Thus, the second or foreign metalbecomes an integral part of the metallic component of the formed ceramicbody.

A predetermined quantity of a second metal is provided to the setupcomprising precursor metal, refractory containment vessel, andoptionally a composite filler material or preform, by (1) pre-processalloying or mixing of the second metal with the precursor metal oremploying a commercially available alloy having a desired composition,(2) applying the second metal on one or more surfaces of the precursormetal, or (3) in cases where a composite is formed, by admixing thesecond metal with the filler or preform material (which techniques arediscussed in greater detail below) such that a desired quantity ofsecond metal will be introduced into the flux of molten precursor metaland transported through the oxidation reaction product which is formedas described in the above-referenced Commonly Owned Patents and PatentApplications. The ceramic body is recovered having a metallic componentcomprising the second metal and unoxidized constituents of the precursormetal. The metallic component of the formed ceramic body isinterconnected and/or isolated metallic inclusions.

In the practice of the present invention, the choice of second metal isbased primarily upon one or more properties sought for the ceramic body.The metal component can impart certain favorable properties to, orimprove the performance of, the formed ceramic body respecting itsintended use. For example, metal in the ceramic body can beneficiallyimprove the fracture toughness, resilience, thermal conductivity,environmental compatibility, and electrical conductivity of the ceramicbody, depending upon such factors as the identity of the metal and theamount and distribution of the metal throughout the microstructure ofthe ceramic product. By providing a method for tailoring theconstituency of the metal to include metals or metallic phases otherthan the precursor metal, the invention adds substantial latitude to theend-use application of such ceramic bodies. In order to impart thedesired property(ies) to the formed ceramic body, the second or foreignmetal remains substantially nonreactive with the vapor-phase oxidant.Therefore, second metals should be chosen which do not form an oxidationreaction product preferentially to the precursor metal under theparticular process conditions. Typically, a second metal satisfies thatcriterion if it has a less negative free energy of formation at a givenreaction temperature than that of the precursor metal, with respect tothe particular oxidation reaction occurring with the vapor-phase oxidantpresent.

However, the second or foreign metal may alloy or react with theprecursor metal within the metallic component to form alloys orintermetallic compounds, which may be desirable, or impart desirableattributes to the resulting ceramic body. Thus, in accordance with thepresent invention, there is also provided a method for the in situformation of one or more desired metallic phases comprising theprecursor metal and the second metal. Such metallic phases (i.e.metallic component) include intermetallic compounds, solid solutions,alloys or combinations of each. In the present embodiment, a suitablesecond metal is selected satisfying the criteria set out above and,additionally, which forms one or more metallic phases in combinationwith the precursor metal, at a given temperature and relativeconcentration, which are desirable to be incorporated into the ceramicbody. The second metal is provided and introduced into the flux ofmolten precursor metal in a lower relative concentration than is neededto form the desired metallic phase. As the molten precursor metal reactswith the vapor-phase oxidant at a given reaction temperature, formingthe oxidation reaction product, the relative concentration of precursormetal within the interconnected metallic constituency is depleted orreduced. Therefore, the relative concentration of the second metalincreases within the metallic constituency of the ceramic body. Thereaction is continued at a given reaction temperature or within atemperature range until a sufficient quantity of precursor metal hasbeen depleted from the constituency leading to the formation of adesired metallic phase, thereby forming or enriching the desiredmetallic phase comprising the precursor metal and second metal; or,alternatively, the oxidation reaction can be continued for a timesufficient to deplete an amount of precursor metal such that on reducingthe reaction temperature, or cooling the formed ceramic product, thedesired metallic phase formation occurs, thus forming or enriching thedesired metallic phase comprising the precursor metal and second metal.The resulting metallic phase can either inherently impart a desirableproperty or properties to the ceramic product, or can be of such acomposition that will form one or more additional phases at a givenservice temperature thereby imparting the desired property or propertiesto the ceramic product. Additionally, by the manipulation of reactionparameters, i.e. reaction time, reaction temperature, etc., or by theappropriate combination or addition of certain metals, the desiredmetallic phase(s) can be further tailored as in, for example,precipitation hardening of a desired alloy within the metalliccomponent.

It should be understood that in the practice of the present invention,it may be necessary to provide a greater quantity of second metal in asetup than is desired or needed to be incorporated into the metalliccomponent of the ceramic body. The amount of second metal which needs tobe provided in the setup in order that the desired quantity of secondmetal will be introduced into the flux of molten precursor metal, andthus be incorporated into the ceramic body, will depend primarily uponthe identities and interactive properties of the second metal andprecursor metal, reaction conditions, and the means by which the secondmetal is provided.

Since the method herein disclosed of incorporating a second metal intothe metallic component of a ceramic product involves the intimatecombination of two or more metals, viz. the second metal and precursormetal, it should be understood that the latitude afforded with respectto the identity, quantity, form, and/or concentration of second metalrelative to the precursor metal to be employed will depend upon themetallic constituents which are desired to be incorporated into theceramic product, and the process conditions necessary for the formationof the oxidation reaction product. The inclusion and/or formation of thedesired metallic constituents will be governed, at least in part, by theproperties and/or physical metallurgy associated with the combination orinteraction of the particular metals present under the particularprocess conditions, and/or the means chosen to provide the second metalfor introduction to the precursor metal. This combination of metals mayeffect the formation of various metallic phases, including alloys,intermetallic compounds, solid solutions, precipitates, or mixtures, andmay be affected by the presence and concentration of impurities ordopant materials. Thus, the constituency resulting from combination ofthe metals in the practice of the present invention can have propertieswhich vary significantly from those of the several metals. Suchcombinations in the form of metallic phases comprising the precursormetal and second metal incorporated into the metallic component of theformed ceramic body can advantageously affect properties of the ceramicproduct. For example, the combination of second metal and precursormetal may form metallic phases such as solid solutions, alloys or one ormore intermetallic compounds which have a melting point above that ofthe precursor metal, thereby expanding the service temperature range ofa ceramic product having such a metallic phase incorporated therein.However, it should be understood that in some cases the melting point ofthe resulting metallic phase or phases may be above the operabletemperature range for the formation of the intended oxidation reactionproduct. Additionally, the formation of metallic phases resulting fromcertain combinations of parent and second metals may impart addedviscosity to the resulting molten metal at the reaction temperature, ascompared with molten precursor metal without the addition of secondmetal at the same temperature, such that the transport of molten metalthrough the formed oxidation reaction product substantially slows ordoes not occur. As such, care should be taken with respect to designinga desired system which includes such a metallic combination in order toensure that the metallic constituency remains sufficiently liquid whilethe oxidation reaction product is being formed to facilitate thecontinued flux of molten metal at a temperature which is compatible withthe parameters of the oxidation reaction process.

When providing the second metal by pre-process alloying with theprecursor metal, or employing a commercially available alloy of desiredcomposition, introduction of the second metal into the flux of moltenmetal is effected by the transport of molten metal from the body ofmolten metal into the formed oxidation reaction product. Thus,introduction will depend upon the constituency of the molten metal whichis transported from the body of molten metal, formed in the heatingstep, into the formed oxidation reaction product. This transportedconstituency will be determined by such factors as the homogeneity ofthe metallic constituency, and the metallic phases associated with theparticular combination of metals chosen at a given reaction temperatureand relative concentration.

In embodiments of the present invention wherein the second metal, orsource of same, is provided external to the precursor metal, additionalparameters should be considered. More specifically, one should considerthe metallurgical properties associated with the contact of the moltenprecursor metal with the second metal in order to effect introduction ofthe desired quantity of second metal into the flux of molten precursormetal. When the second metal is provided external to the precursor metalbody, introduction may be effected on contact of the molten precursormetal with the second metal by dissolution of one metal into the other,interdiffusion of the two metals, or reaction of the two metals as inthe formation of one or more intermetallic compounds or other metallicphases between the precursor metal and second metal. Thus, theintroduction and/or rate of introduction of second metal into the fluxof molten precursor metal will depend on one or more of several suchmetallurgical factors. Such factors include the physical state of thesecond metal at the particular reaction temperature, the rate ofinterdiffusion between the precursor metal and second metal, the degreeand/or rate of solubility of the second metal into the precursor metalor the precursor metal into the second metal, and the formation ofintermetallics or other metallic phases between the precursor metal andsecond metal. Thus, care should be taken to ensure that the reactiontemperature is maintained such that the metallic constituency, resultingfrom the introduction of second metal into the flux of molten precursormetal, remains at least partially liquid to facilitate the transport ofthe metallic constituency into the formed oxidation reaction product,and thus enable contact of the molten precursor metal with thevapor-phase oxidant in order to facilitate growth of the ceramic body.In accordance with the present invention, the introduction of secondmetal into the flux of molten precursor metal, or the depletion ofprecursor metal from the flux of molten metal due to formation of theoxidation reaction product, can result in a constituency or metallicphase formation which effects the formation of one or more metallicphases comprising the precursor metal and second metal. However, certaincombinations of precursor metal and second metal may impart significantviscosity to the flux, or otherwise impede the flux of molten metal suchthat transport of metal toward the vapor-phase oxidant ceases prior tothe complete development of the desired oxidation reaction product. Insuch cases, the formation of the desired oxidation reaction product maybe halted or substantially slowed by those phenomena and, therefore,care should be exercised to avoid the premature formation of suchconstituents.

As explained above in accordance with the present invention, the desiredquantity of a second or foreign metal may be provided by alloying withthe precursor metal prior to the fabrication process. For example, in asystem wherein aluminum (or an aluminum-based metal) is the precursormetal employing air as the vapor-phase oxidant to form an aluminaoxidation reaction product, second metals such as titanium, copper,nickel, silicon, iron, or chromium may be alloyed, in amounts which maybe limited and/or dictated as discussed above, with the aluminumprecursor metal. Additional second or foreign metals include aluminum,zirconium, hafnium, cobalt, manganese, germanium, tin, silver, gold, andplatinum. It may be desirable, for example, to include copper, or ametallic phase including copper, in the metallic component of theceramic body. In order for the metallic component to impart one or moreproperties to, or improve the performance of, a ceramic body, it isdesirable that properties of the particular metal, combination of metalsor metallic phase incorporated into the metallic component do notsubstantially degrade at the service temperature of the ceramic product.Certain aluminum-copper metallic phases, for example, Cu₉ Al₄, have aservice temperature range which is higher than that of aluminum. Thus,by incorporating or enriching such a phase within the interconnectedmetallic component of the ceramic, the improved performance of theceramic due to the presence of the metallic component will be exhibitedat increased service temperatures. To incorporate a suitable quantity ofcopper in order to effect the desired phase transformation(s) to obtainthe desired aluminum-copper metallic phase Cu₉ Al₄, the copper may bealloyed with the aluminum precursor metal, for example, at 10% by weightof the total copper-aluminum alloy. The alloy comprising the aluminumprecursor metal and the second metal copper is heated below the meltingpoint of the intended oxidation reaction product, alumina, but above themelting point of the copper-aluminum alloy (as described inabove-referenced Commonly Owned Patents and Patent Applications). Whenthe molten aluminum precursor metal is contacted with the oxidant, thereis formed a layer comprising alumina as the oxidation reaction product.Molten alloy is then transported through the formed oxidation reactionproduct, towards the oxidant. As the molten alloy contacts the airoxidant, the aluminum metal constituent of the alloy is at leastpartially oxidized thus forming a progressively thicker layer ofoxidation reaction product. The second or foreign metal copper, alsobeing a constituent of the molten alloy, is likewise transported intothe formed oxidation reaction product. However, since the copper is notdepleted from the ceramic body by the vapor-phase oxidation, therelative concentration of the copper increases as the aluminum isoxidized and thus depleted from the flux of molten metal. The oxidationof the aluminum metal is continued for a time sufficient to achieve theappropriate metallic constituency for the formation of the desiredmetallic phases. Referring to a binary metallic phase diagram for acopper aluminum system, the Cu₉ Al₄ phase is formed in a relativeconcentration range of approximately 80-85% copper, balance aluminum, ina service temperature range for the ceramic product not exceedingapproximately 780° C.

Where the desired quantity of second or foreign metal is applied, as inlayering, or contacted with, one or more surfaces of an aluminumprecursor metal, and the precursor metal is reacted with air as thevapor-phase oxidant, suitable second metals, include for example,silicon, nickel, titanium, iron, copper, or chromium, preferably inpowder or particulate form. For example, nickel or a metallic phasecontaining nickel may be a desirable constituent in a ceramic productfabricated in accordance with the present invention. Nickel-aluminideintermetallics such as NiAl, Ni₂ Al₃ or NiAl₃ might be desirable toimprove the corrosion resistance of the metallic component of theceramic body. Therefore, in order to effect the introduction of asuitable quantity of nickel to form or enrich the desirednickel-aluminum metallic phases, a predetermined quantity of powderednickel metal is dispersed over the growth surface of the aluminumprecursor metal body. As the molten aluminum precursor metal contactsthe nickel metal, an amount of the nickel metal is introduced into theflux of molten aluminum precursor metal. The introduced nickel metal isthen transported, as a constituent of the flux of molten metal, into thealumina oxidation reaction product. Analogous to the copper exampleabove, as the aluminum metal is oxidized, the relative concentration ofnickel metal within the forming ceramic body increases, the appropriatecomposition is achieved to form the desired phases.

Where the product is a ceramic composite, fabricated by growing theoxidation reaction product into a mass or aggregate of filler material,or a permeable preform, placed adjacent to the precursor metal, thesecond or foreign metal may be provided by admixing with the fillermaterial or preform material, or applied, as in layering, to one or moresurfaces of same. For example, if the desired composite productcomprises an alumina ceramic matrix, fabricated by the vapor-phaseoxidation of aluminum precursor metal into a bed of silicon carbideparticles, which may be preformed into a green body, powders orparticles of second metals such as titanium, iron, lead, nickel, copper,chromium, or silicon can be admixed with the silicon carbide fillermaterial. For example, it may be desirable to incorporate an amount ofsilicon into the ceramic body in order to improve the compatibility ofthe metallic component of the composite ceramic body with hightemperature applications. Therefore, a quantity of silicon metal, whichmay be limited or governed as discussed above, is admixed with thesilicon carbide filler material. As the formed alumina oxidationreaction product embeds the silicon carbide particles, and the moltenaluminum is transported therethrough, the molten aluminum metal contactsthe admixed silicon metal. A quantity of silicon metal is thusintroduced into the continued flux of molten metal, and thus into theforming ceramic composite body. In the present embodiment, the portionof the second metal which is not introduced into the flux of moltenmetal, but is included in that portion of the mass of filler or preformwhich is infiltrated by the oxidation reaction product, may be presentin the composite body as isolated inclusions of second metal. The secondor foreign metal may also be applied on only one or more surfaces of amass or aggregate of filler or shaped preform. For this compositeexample, the silicon particulate or powder is applied as a layer onto asurface of the silicon carbide particles or a preform comprisingparticles of same. As the flux of molten aluminum precursor metalcontacts this surface, a quantity of silicon metal is introduced intothe flux and becomes a part of the metallic component in the recoveredceramic product. Application of second metal to one or more surfaces ofa mass of filler or preform in accordance with the present embodimentcan result in a composite body wherein the exposed portions of themetallic component are rich in the second or foreign metal relative toother portions of metallic component within the formed ceramic compositebody.

In the practice of the present invention wherein the second or foreignmetal is provided external to the precursor metal, the second or foreignmetal can be provided in the form of a mixture or compound which willreact with the molten metal, and/or dissociate under the processconditions, to liberate the second or foreign metal which is thenintroduced, as discussed above, into the flux of molten metal. Such acompound may be a metal oxide which is reducible by, or will react, withthe precursor metal to liberate the second metal. For example, if aceramic composite body is desired comprising an alumina ceramic matrix,fabricated by the oxidation of aluminum precursor metal, embeddingparticles of alumina filler material, an oxide of a desired second metalsuch as silicon, nickel, iron, or chromium may be admixed with thealumina bedding material, or layered on top of the aluminum precursormetal. For example, if chromium is desired as a second metal, chromiummetal can be introduced into the flux of molten metal by admixing chromeoxide with a bedding material. When the flux of the molten aluminumcontacts the chrome oxide, the molten aluminum will reduce the chromeoxide and liberate chromium metal. A quantity of the liberated chromiummetal is then introduced into the flux of molten aluminum, as discussedabove, and transported through and/or into the oxidation reactionproduct which is formed as the molten aluminum precursor metal continuesto contact the vapor-phase oxidant.

As explained in the Commonly Owned Patents and Patent Applications,dopant materials, used in conjunction with the precursor metal,favorably influence the oxidation reaction process, particularly insystems employing aluminum as the precursor metal. Additionally, in thepractice of the present invention, in certain cases a dopant materialmay be chosen to, in addition to its doping qualities, provide a secondor foreign metal or a source of same which is desirous to beincorporated into the metallic component of the ceramic product. Forexample, silicon is a useful dopant material and can also impartdesirable characteristics to the metallic component of the ceramic bodysuch as improved high temperature performance in certain systems.Therefore, silicon can be employed in elemental form, or as silicondioxide, in accordance with the above embodiment, to serve the dualpurpose of acting as a dopant material and supplying a source of secondmetal. However, in some cases, a suitable dopant material will not beavailable which supplies both the necessary doping characteristics and asource of the desired second or foreign metal. Therefore, a dopantmaterial will need to be used in conjunction with the second or foreignmetal. It should be noted, however, that when employing a dopantmaterial in conjunction with a second metal, the presence of each mayhave an effect upon the function and/or performance of the other. Thus,in practicing the embodiment of the present invention wherein it isdesirable to effect the formation of one or more metallic phasescomprising the precursor metal and second metal, and, additionally, aseparate dopant material is employed, the respective concentrations ofprecursor metal and second metal necessary to effect formation of thedesired phases(s) may be different than the concentrations necessary toeffect formation of the phases in the binary system comprising theprecursor metal and second metal. Therefore, care should be taken toconsider the effect of all metals present in a specific case whendesigning a system wherein it is desired to effect the formation of oneor more metallic phases within the metallic component of the ceramicbody. The dopant or dopants used in conjunction with the precursormetal, as in the case of second metals, (1) may be provided as alloyingconstituents of the precursor metal, (2) may be applied to at least aportion of the surface of the precursor metal, or (3) may be applied toor incorporated into part or all of the filler material or preform, orany combination of two or more techniques (1), (2), or (3) may beemployed. For example, an alloyed dopant may be used solely or incombination with a second externally applied dopant. In the case oftechnique (3), wherein additional dopant or dopants are applied to thefiller material, the application may be accomplished in any suitablemanner as explained in the Commonly Owned Patents and PatentApplications.

The function or functions of a particular dopant material can dependupon a number of factors. Such factors include, for example, theparticular combination of dopants when two or more dopants are used, theuse of an externally applied dopant in combination with a dopant alloyedwith the precursor metal, the concentration of dopant employed, theoxidizing environment, process conditions, and as stated above, theidentity and concentration of the second metal present.

Dopants useful for an aluminum precursor metal, particularly with air asthe oxidant, include magnesium, zinc, and silicon either alone or incombination with each other or in combination with other dopants, asdescribed below. These metals, or a suitable source of the metals, maybe alloyed into the aluminum-based precursor metal at concentrations foreach of between about 0.1-10% by weight based on the total weight of theresulting doped metal. These dopant materials or a suitable sourcethereof (e.g. MgO, ZnO, or SiO₂) may be used externally to the precursormetal. Thus an alumina ceramic structure is achievable for the aluminumprecursor metal using air as the oxidant by using MgO as a dopant in anamount greater than about 0.0008 gram per gram of precursor metal to beoxidized and greater than 0.003 gram per square centimeter of precursormetal upon which to MgO is applied. However, the concentration of dopantneeded, as discussed above, may depend upon the identity, presence, andconcentration of a second or foreign metal.

Additional examples of dopant materials for aluminum precursor metalinclude sodium, germanium, tin, lead, lithium, calcium, boron,phosphorus, and yttrium which may be used individually or in combinationwith one or more dopants depending on the oxidant, identity and quantityof second or foreign metal present and process conditions. Rare earthelements such as cerium, lanthanum, praseodymium, neodymium, andsamarium are also useful dopants, and herein again especially when usedin combination with other dopants. All of the dopant materials, asexplained in the Commonly Owned Patents and Patent Applications, areeffective in promoting polycrystalline oxidation reaction growth for thealuminum-based precursor metal systems.

As disclosed in commonly owned U.S. Pat. No. 4,923,832, which issued onMay 8, 1990, from U.S. patent application Ser. No. 861,024, filed May 8,1986 (discussed above herein), and assigned to the same assignee, abarrier means may be used to inhibit growth or development of theoxidation reaction product beyond the barrier. Suitable barrier meansmay be any material, compound, element, composition, or the like, which,under the process conditions of this invention, maintains someintegrity, is not volatile, and preferably is permeable to thevapor-phase oxidant while being capable of locally inhibiting,poisoning, stopping, interfering with, preventing, or the like,continued growth of oxidation reaction product. Suitable barriersinclude calcium sulfate (Plaster of Paris), calcium silicate, andPortland cement, and combinations thereof, which typically are appliedas a slurry or paste to the surface of the filler material. Thesebarrier means also may include a suitable combustible or volatilematerial that is eliminated on heating, or a material which decomposeson heating, in order to increase the porosity and permeability of thebarrier means. Still further, the barrier means may include a suitablerefractory particulate to reduce any possible shrinkage or crackingwhich otherwise may occur during the process. Such a particulate havingsubstantially the same coefficient of expansion as that of the fillerbed is especially desirable. For example, if the preform comprisesalumina and the resulting ceramic comprises alumina, the barrier may beadmixed with alumina particulate, desirably having a mesh size of about20-1000. Other suitable barriers include refractory ceramics or metalsheaths, which are open on at least one end to permit the vapor-phaseoxidant to permeate the bed and contact the molten precursor metal. Incertain cases, it may be possible to supply a source of second metalwith the barrier means. For example, certain grades of stainless steelcompositions, when reacted under certain oxidizing process conditions asat a high temperature in an oxygen-containing atmosphere, form theircomponent oxides such as iron oxide, nickel oxide, or chromium oxidedepending on the composition of the stainless steel. Thus, in somecases, a barrier means such as a stainless steel sheath may provide asuitable source of second or foreign metal, and which may effectintroduction of second metals such as iron, nickel, or chromium into theflux of molten metal on contact of same.

EXAMPLE 1

In accordance with the present invention, an alumina ceramic body wasfabricated such that the metal component contained copper-aluminumintermetallic compounds. Thus, copper was provided as a second metal aspre-process alloy addition to the precursor metal body.

A 2×1×1/2 inch bar of an aluminum alloy comprising 10 weight percentcopper and 3 weight percent magnesium (a dopant), balance aluminum, wasplaced into a bed of alumina particles (El Alundum, from Norton Co., 90mesh), which was contained in a refractory vessel, such that a 2×1 inchface of the bar was exposed to the atmosphere and substantially flushwith the bed. A thin layer of silicon dioxide dopant material wasuniformly dispersed over the exposed surface of the bar. This setup wasplaced into a furnace and heated up over 5 hours to 1400° C. The furnacewas held at 1400° C. for 48 hours, and then cooled down over 5 hours toambient. The setup was removed from the furnace, and the ceramic bodywas recovered.

The ceramic structure was cross-sectioned for metallographic and phaseanalyses. X-ray diffraction analysis of the metallic component of theceramic showed Cu₉ Al₄ copper-aluminum intermetallic present toward thetop of the structure, and CuAl₂ copper-aluminum intermetallic andnon-oxidized aluminum toward the initial growth of the ceramic.

EXAMPLE 2

Ceramic composite materials with an aluminum-based metallic constituentenriched in nickel are prepared to determine whether such materialswould have enhanced mechanical characteristics. The procedure followedin preparing these materials involved the use of sedimentation castingto make preforms of aluminum oxide particles containing metallic nickelpowder. These preforms were subsequently infiltrated with an aluminumoxide ceramic matrix which interacted with the nickel powder to form ametallic constituent enriched in nickel.

In more detail, either 10% or 30% by weight of nickel metal powder wasadded to a mixture of aluminum oxide powders (Norton 38 Alundum)consisting of 70% 220 mesh and 30% 500 mesh particle sizes. Theresulting blend of oxide and metal particles was slurried in watercontaining also 2% by weight of an polyvinyl acetate latex binder(Elmer's Wood Glue). The ratio of powder to water (plus binder) was2.5:1 by weight. Preforms were prepared by pouring the slurry into 2inch by 2 inch square molds and allowing the solid particles to settleinto a layer approximately 1/2 inch thick. Excess water in the castingprocess is poured and sponged from the surface.

Each preform was assembled with a 2×2×1/2 inch bar of aluminum alloy380.1 along a 2×2 inch common surface with a thin layer of siliconpowder placed on the interface as a dopant to promote the oxidationreaction. The 380.1 alloy lot used in these experiments was found bychemical analysis to be consistent with the nominal specification forthis alloy (i.e., 7.5-9.5% Si, 3.0-4.0% Cu, <2.9% Zn, <1.50% Fe, <0.5%Mn, <0.5% Ni, <0.35% Sn, and <0.1% Mg), except that the Mg concentrationwas found to be approximately 0.17% to 0.18% by weight. The higher Mglevel is believed to be important in view of the established role of Mgas a dopant or promoter of the oxidation reaction.

The metal/preform assemblies were placed individually in inertrefractory boats and surrounded on all sides by a layer of wollastoniteparticles. Each served as a barrier material to confine the oxidationreaction to the volume contained within the preform. The refractoryboats with their contents were placed in a furnace and heated in air at1000° C. for 80 hours.

Upon removal from the furnace it was found that an aluminum oxideceramic matrix had grown from the surface of the molten aluminum alloyand infiltrated the preform. Metallographic examination of crosssections of these materials showed particles of the filler material (38Alundum) bonded together by an aluminum oxide matrix containing ametallic constituent comprised of aluminum (from the parent metal),silicon (from the parent metal and the dopant layer) and nickel (fromthe nickel powder added to the preform), plus other minor constituentsof the parent metal.

Mechanical properties measurements were obtained on specimens preparedfrom these ceramic composite materials. Most noteworthy was an increasein the toughness of the material containing nickel, as determined by astandard chevron notch toughness test. Thus, the material prepared fromthe preform with 10% nickel yielded an average toughness value of 8.5MPa-m^(1/2) while that formed from the 30% nickel preform gave anaverage toughness of 11.3 MPa-m^(1/2). From prior experience withsimilar materials, toughness values only in the range of 4-7 in the sameunits would be expected in the absence of the nickel addition.

What is claimed is:
 1. A method for producing a ceramic body comprisingan oxidation reaction product obtained by oxidation of a precursor metalto form a polycrystalline material comprising (i) an oxidation reactionproduct of said precursor metal with a vapor-phase oxidant, and (ii) ametallic component, said method comprising the steps of:(a) heating asource of precursor metal in the presence of a vapor-phase oxidant to atemperature above the melting point of said precursor metal but belowthe melting point of its oxidation reaction product to form a body ofmolten precursor metal; (b) reacting said body of molten precursor metalwith said vapor-phase oxidant at said temperature to permit saidoxidation reaction product to form; and inducing a flux of molten metalwithin said oxidation reaction product, said flux comprising said moltenprecursor metal and at least one second metal, wherein a primaryconstituent of said at least one second metal comprises at least onematerial selected from the group consisting of titanium, iron, nickel,copper, zirconium, hafnium, cobalt, manganese, silver, gold and platinumand wherein said second metal is present in an amount greater than about2.0% by weight of said parent metal when the formation of said oxidationreaction product is begun; (c) maintaining at least a portion of saidoxidation reaction product in contact with and between said moltenprecursor metal and said vapor-phase oxidant at said temperature toprogressively draw molten precursor metal through said oxidationreaction product towards said vapor-phase oxidant to permit freshoxidation reaction product to continue to form at an interface betweensaid vapor-phase oxidant and previously formed oxidation reactionproduct, said maintaining being continued for a time sufficient todeplete said precursor metal in said flux relative to said at least onesecond metal to result in formation or enrichment of at least onemetallic phase comprising at least said second metal; and (d) continuingstep (c) at said temperature for a time sufficient to form said ceramicbody comprising (a) said oxidation reaction product; and (b) a metalliccomponent comprising said at least one metallic phase; and (e)recovering said formed ceramic body, whereby said at least one metallicphase is present in a significant quantity such that at least oneproperty of the formed ceramic body is effected by said at least onemetallic phase.
 2. A method for producing a ceramic composite bodycomprising infiltrating a porous body with an oxidation reaction productobtained by oxidation of a precursor metal to form a polycrystallinematerial comprising (i) an oxidation reaction product of said precursormetal with a vapor-phase oxidant, and (ii) a metallic component, saidmethod comprising the steps of:(a) forming at least one porous body tobe infiltrated, said at least one porous body comprising a body selectedfrom the group consisting of a permeable mass of filter material an apermeable preform; (b) orienting said at least one porous body and asource of precursor metal relative to each other so that formation ofsaid oxidation reaction product of said precursor metal will occur intosaid at least one porous body and towards said vapor-phase oxidant; (c)heating said source of precursor metal and said at least one porous bodyin the presence of said vapor-phase oxidant to a temperature above themelting point of said precursor metal but below the melting point of itsoxidation reaction product to form a body of molten precursor metal; (d)reacting said body of molten precursor metal with said vapor-phaseoxidant at said temperature to permit said oxidation reaction product toform; and inducing a flux of molten metal within said oxidation reactionproduct, said flux comprising said molten precursor metal and at leastone second metal, wherein a primary constituent of said at least onesecond metal comprises at least one material selected from the groupconsisting of titanium, iron, nickel, copper, zirconium, hafnium,cobalt, manganese, silver, gold and platinum and wherein said secondmetal is present in an amount greater than about 2.0% by weight of saidparent metal when the formation of oxidation reaction product is begun;(e) maintaining at least a portion of said oxidation reaction product incontact with and between said molten precursor metal and saidvapor-phase oxidant at said temperature to progressively draw moltenprecursor metal through said oxidation reaction product towards saidvapor-phase oxidant to permit fresh oxidation reaction product tocontinue to form at an interface between said vapor-phase oxidant andpreviously formed oxidation reaction product that has unfiltrated saidat least one body; (f) continuing step (e) at said temperature for atime sufficient to infiltrate at least a portion of said at least oneporous body with said polycrystalline material, thereby forming saidceramic composite body comprising (a) said oxidation reaction product;(b) said at least one porous body; and (c) a metallic componentcomprising at least one metallic phase; and (g) recovering said formedceramic composite body, whereby said at least one metallic phase ispresent in a significant quantity such that at least one property of theformed ceramic composite body is effected by said at least one metallicphase.
 3. A method for producing a ceramic body comprising an oxidationreaction product obtained by oxidation of a precursor metal to form apolycrystalline material comprising (i) an oxidation reaction product ofsaid precursor metal with a vapor-phase oxidant, and (ii) a metalliccomponent, said method comprising the steps of:(a) heating a source ofprecursor metal in the presence of a vapor-phase oxidant to atemperature above the melting point of said precursor metal but belowthe melting point of its oxidation reaction product to form a body ofmolten precursor metal; (b) reacting said body of molten precursor metalwith said vapor-phase oxidant at said temperature to permit saidoxidation reaction product to form; and inducing a flux of molten metalwithin said oxidation reaction product, said flux comprising said moltenprecursor metal and at least one second metal, wherein said at least onesecond metal is present in a quantity greater than about 10% by weightof said parent metal when the formation of said oxidation reactionproduct is begun; (c) maintaining at least a portion of said oxidationreaction product in contact with and between said molten precursor metaland said vapor-phase oxidant at said temperature to progressively drawmolten precursor metal through said oxidation reaction product towardssaid vapor-phase oxidant to permit fresh oxidation reaction product tocontinue to form at an interface between said vapor-phase oxidant andpreviously formed oxidation reaction product, said maintaining beingcontinued for a time sufficient to deplete said precursor metal in saidflux relative to said at least one second metal to result in formationor enrichment of at least one metallic phase comprising at least saidsecond metal; (d) continuing step (c) at said temperature for a timesufficient to form said ceramic body comprising (i) said oxidationreaction product; and (ii) a metallic component comprising said at leastone metallic phase; and (e) recovering said formed ceramic body, wherebysaid at least one metallic phase is present in a significant quantitysuch that at least one property of the formed ceramic body is effectedby said at least one metallic phase.
 4. A method for producing a ceramiccomposite body comprising infiltrating a porous body with an oxidationreaction product obtained by oxidation of a precursor metal to form apolycrystalline material comprising (i) an oxidation reaction product ofsaid precursor metal with a vapor-phase oxidant, and (ii) a metalliccomponent, said method comprising the steps of:(a) forming at least oneporous body to be infiltrated, said at least one porous body comprisinga body selected from the group consisting of a permeable mass of fillermaterial and a permeable preform; (b) orienting said at least one porousbody and a source of precursor metal relative to each other so thatformation of said oxidation reaction product of said precursor metalwill occur into said at least one porous body and towards saidvapor-phase oxidant; (c) heating said source of precursor metal and saidat least one porous body in the presence of said vapor-phase oxidant toa temperature above the melting point of said precursor metal but belowthe melting point of its oxidation reaction product to form a body ofmolten precursor metal; (d) reacting said body of molten precursor metalwith said vapor-phase oxidant at said temperature to permit saidoxidation reaction product to form; and inducing a flux of molten metalwithin said oxidation reaction product, said flux comprising said moltenprecursor metal and at least one second metal, wherein said at least onesecond metal is present in a quantity greater than about 10% by weightof said parent metal when the formation of said oxidation reactionproduct is begun; (e) maintaining at least a portion of said oxidationreaction product in contact with and between said molten precursor metaland said vapor-phase oxidant at said temperature to progressively drawmolten precursor metal through said oxidation reaction product towardssaid vapor-phase oxidant to permit fresh oxidation reaction product tocontinue to form at an interface between said vapor-phase oxidant andpreviously formed oxidation reaction product that has infiltrated saidat least one body; (f) continuing step (e) at said temperature for atime sufficient to infiltrate at least a portion of said at least oneporous body with said polycrystalline material, thereby forming saidceramic composite body comprising (i) said oxidation reaction product;(ii) said at least one porous body; and (iii) a metallic componentcomprising at least one metallic phase; and (g) recovering said formedceramic composite body, whereby said at least one metallic phase ispresent in a significant quantity such that at least one property of theformed ceramic composite body is effected by said at least one metallicphase.
 5. The method of claim 1, claim 2, claim 3 or claim 4, whereinsaid at least one second metal is alloyed with said precursor metalprior to said heating step, whereby said second metal is incorporatedinto said molten flux.
 6. The method of claim 1, claim 2, claim 3 orclaim 4, wherein said at least one second metal is added to saidprecursor metal by applying a layer of said at least one second metal toat least one external surface of said precursor metal prior to saidheating step, whereby said second metal is incorporated into said moltenflux.
 7. The method of claim 2 or claim 4, wherein said at least onesecond metal is applied to one surface of said at least one porous bodyto be infiltrated, whereby said second metal is incorporated into saidmolten flux.
 8. The method of claim 1, claim 2, claim 3 or claim 4wherein said at least one metallic phase is dispersed substantiallyuniformly throughout said metallic component.
 9. The method of claim 1,claim 2, claim 3 or claim 4, wherein said at least one metallic phasesis substantially concentrated in a portion of said metallic component.10. The method of claim 5, wherein said at least one second metalcomprises a metal-containing compound which is dissociated into at leasta metal ion under the process conditions set forth in said reacting stepto liberate said at least one metal ion as said at least one secondmetal.
 11. The method of claim 1, claim 2, claim 3 or claim 4, wherein avolume percent of said metallic component is about 1-40%.
 12. The methodof claim 1, claim 2, claim 3 or claim 4, wherein said oxidation reactionis continued for a time sufficient to effect formation of said at leastone metallic phase at said temperature in said reacting step.
 13. Themethod of claim 1, claim 2, claim 3 or claim 4, wherein said oxidationreaction is continued for a time sufficient to deplete said precursormetal in said flux relative to said at least one second metal to effectformation of said at least one metallic phase below said temperature insaid reacting step.
 14. The method of claim 1, claim 2, claim 3 or claim4, wherein at least one dopant is used in conjunction with saidprecursor or metal.
 15. The method of claim 1, claim 2, claim 3 or claim4, wherein said precursor metal comprises an aluminum precursor metal,said vapor-phase oxidant comprises air, and said oxidation reactionproduct comprises alumina.
 16. The method of claim 3 or claim 4, whereina primary constituent of said second metal comprises a material selectedfrom the group consisting of aluminum, titanium, iron, nickel, copper,zirconium, hafnium, cobalt, manganese, silicon, germanium, tin, silver,gold and platinum.
 17. The method of claim 6, wherein said at least onesecond metal comprises a metal-containing compound which is dissociatedinto at least a metal ion under the process conditions set forth in saidreacting step to liberate said at least one metal ion as said at leastone second metal.
 18. The method of claim 7, wherein said at least onesecond metal comprises a metal-containing compound which is dissociatedinto at least a metal ion under the process conditions set forth in saidreacting step to liberate said at least one metal ion as said at leastone second metal.
 19. The method of claim 2 or claim 4, wherein said atleast one second metal comprises a metal-containing compound which isdissociated into at least one metal ion under the process conditions setforth in said reacting step to liberate said at least one metal ion assaid at least one second metal.
 20. The method of claim 1, claim 2,claim 3 or claim 4, wherein said at least one second metal has anegative free energy of formation at said temperature in said reactingstep which is less than the negative free energy of formation of saidoxidation reaction product.
 21. The method of claim 1, claim 2, claim 3or claim 4, wherein said at least one property which is effectedcomprises at least one property selected from the group consisting offracture toughness, thermal conductivity, environmental compatibilityand electrical conductivity.
 22. The method of claim 3 or claim 4,wherein at least one dopant is used in conjunction with said precursormetal, said at least one dopant functioning as both a dopant materialand a source of said at least one second metal.
 23. The method of claim3 or claim 4, wherein a primary constituent of said at least one secondmetal comprises at least one material selected from the group consistingof silicon, germanium and tin.
 24. The method of claim 23, wherein saidat least one material functions as both a dopant material and a sourceof said at least one second metal.